2,7-dimethyl-2,4,6-octatriene-1,8-dialdehyde (abbreviation: C-10 dialdehyde), is basically a light-yellow powder solid with a melting point of 157.0˜159.0° C., and freely soluble in methanol and dichloromethane, and soluble in petroleum ether and ethyl acetate, and slightly soluble in water. C-10 dialdehyde has no special smell, and is stable at room temperature, and easily changes with a mixture of oxidant, and usually kept isolated from air. C-10 dialdehyde is a key intermediate to synthesize carotenoids compounds such as β-carotene, canthaxanthin and astaxanthin, lycopene, etc. Studies on processes of synthesizing C-10 dialdehyde is more important with widespread applications of carotenoids.
Several synthetic methods reported in the prior documents are shown as follows. Route 1: furan as a raw material reacts with methanol to produce 1,1,4,4-tetramethoxy-2-butene via two steps of addition reaction, condense the diacetal compound with propenyl ether catalyzed with Lewis acid to prepare a C10 skeleton, and then eliminate methanol and form double bond to produce the product through a treatment with base. The key technology of this route is that bromine has higher cost and large toxicity, and the chemical property is active and unstable, the side reaction with acetal is more in addition reaction, for example, the addition product still has diacetal structure. It can occur telomerization to form polymer further through condensing with propenyl ether. So controlling and separating technology of this reaction step is a key for the whole route. The particular reaction scheme is shown as Reaction Equation 1 (synthetic route 1 of C-10 dialdehyde).

Route 2: 1-ethoxy-1-propene as a raw material is added with triethyl orthoformate catalyzed with Lewis acid to prepare 1,1,3,3-tetraethoxy-2-methylpropane, and then eliminate one molecule of ethanol to form 2-methyl-3-ethoxyl-2-crotonaldehyde compound under effects of acid, and undergo an addition reaction with acetylene di-Grignard reagent, and then dehydrate to form ethylenic bond, triple bond hydrogenating to form double bond, and deprotect finally. There are seven steps to synthesize C-10 dialdehyde, and so the reaction steps are long in this process, the reaction control on the first three steps is mainly more difficult. The total yield of C-10 dialdehyde is only 21%. The particular reaction scheme is shown as Reaction Equation 2 (synthetic route 2 of C-10 dialdehyde).

Route 3: 4-acetoxy-2-methyl-2-butene-1-aldehyde (abbreviation: C5 aldehyde) as a raw material for synthesis of vitamin A and neopentyl glycol is formed a acetal protector, and then hydrolyzed with base to produce a hydroxy compound, and halogenate the hydroxy compound, and react with sodium sulphide to form a thioether compound, and convert the thioether compound to sulfoxide via oxidation, and then react with sodium dithionite to produce the product through desulfuration, dimerization and condensation. The particular reaction scheme is shown as Reaction Equation 3 (synthetic route 3 of C-10 dialdehyde).

Route 4: sodium benzene sulfinate salt as a bridging agent reacts with two molecular of 2-(3-chloro-1-methyl-1-propenyl)-5,5-dimethyl-1,3-dioxane to produce sulphone compound, and then eliminate phenylsulfonyl through a strong base to obtain C-10 dialdehyde. In fact, the raw material of chloride is used as the same as that of Route 3, and can also be obtained from 4-acetoxy-2-methyl-2-butene-1-aldehyde as a raw material for synthesis of vitamin A, via three steps reaction of acetal protection, basic hydrolysis, and halogenation. The yield of this reaction route is lower, and the total yield is only 15%. The particular reaction scheme is shown as Reaction Equation 4 (synthetic route 4 of C-10 dialdehyde).

Route 5: propionaldehyde is condensed with methyl formate, and then esterified to prepare 2-methyl-3-alkoxy-2-propenal, the following several reaction steps are basically the same as that of route 2,2-methyl-3-alkoxy-2-propenal is added with acetylene di-Grignard reagent, and deoxidizing triple bond to a double bond, and then form a conjugated double bond through dehydration to obtain C-10 dialdehyde. The particular reaction scheme is shown as Reaction Equation 5 (synthetic route 5 of C-10 dialdehyde).

Route 6: 4-acetoxy-2-methyl-2-butenyl as a raw material is synthesized to 3-(5,5-dimethyl-1,3-dioxane-2-yl)-2-butenal through aldehyde group protection, ester exchange reaction, and oxidation; 2-(3-hydroxyl-methyl-propenyl)-5,5-dimethyl-1,3-dioxane is catalyzed and oxidized through cuprous chloride, 1-oxyl-2,2,6,6-tetramethyl-4-hydroxyl-piperidine (TEMPO) to synthesize 3-(5,5-dimethyl-1,3-dioxane-2-yl)-2-butenal; 2-(3-hydroxyl-1-methyl-1-propenyl)-5,5-dimethyl-1,3-dioxane is chlorinated to synthesize 2-(3-chloro-1-methyl-1-propenyl)-5,5-dimethyl-1,3-dioxane; C-10 triene dialdehyde is obtained through the one-pot process of 3-(5,5-dimethyl-1,3-dioxane-2-yl)-2-butenal, 2-(3-chloro-1-methyl-1-propenyl)-5,5-dimethyl-1,3-dioxane and triethyl phosphite. The particular reaction scheme is shown as Reaction Equation 6 (synthetic route 6 of C-10 dialdehyde).

Route 7: 1,4-dihalo-2-butene as a raw material is rearranged to produce disphosphonate compound through Abrozov, and then undergo a Wittig-Horner reaction with acetone dimethyl acetal through deprotection to produce C10 dialdehyde. It was reported that the total yield is 39%[113,121], and the deficiency is that 1,4-dichloro-2-butene or 1,4-dibromo-2-butene as a raw material cannot have a large-scale localization. The particular reaction scheme is shown as Reaction Equation 7 (synthetic route 7 of C10 dialdehyde).

Route 8: NHU Co., Ltd. improves the synthetic method of C10 olefine aldehyde, wherein trans-1,4-dichloro-2-butene as a raw material is synthesized to 2,7-dimethyl-2,4,6-octatriene-1,8-dialdehyde (C10 olefine aldehyde) via Grignard reaction, condensation reaction and acidic hydrolysis reaction. The particular reaction scheme is shown as Reaction Equation 8 (synthetic route 8 of C10 dialdehyde).

Analyzing the above routes, liquid bromine of route 1 has pollution and large toxicity, the chemical property of allyl methyl ether is active and unstable and easy to produce peroxide which leads to explosion hazard. Route 2 uses acetylene di-Grignard reagent and triple bond partially hydrogenating, and the total yield is only 21%, and consequently is not suitable for industrial production. Both of Route 3 and 4 use 4-acetoxy-2-methyl-2-butene-1-aldehyde as starting material which leads to higher cost and poor economy. The huge deficiency of Route 3 and Route 4 is the biggest obstacle for the industrialization. In Route 5, methyl ether, propionaldehyde, acetylene and dimethyl sulfate are common chemical materials, but it is much easier for propionaldehyde to occur Adol reaction by itself when undergoing Claisen condensation reaction with methyl ether, because of less product and more by-product coming from self condensation, and consequently it has greater difficulty for the separation of product from raw materials and by-products. TEMPO of Route 6 has high cost, and consequently it is difficult to separate raw materials and product when utilizing DNF as solvent. Both of Route 7 and 8 use 1,4-dichlorobutylene as a raw material and is condensed with acetone dimethyl acetal via witting and Grignard reaction, but it has high cost to produce acetone dimethyl acetal, and the di-Grignard reagent prepared by 1,4-dichlorobutylene is extremely unstable, and consequently is not suitable to broadcast in production.